Question
$f(x) = \frac{x}{{1 + {x^2}}}$ $dx$=
$ \Rightarrow 2x\,dx = dt \Rightarrow x\,dx = dt2$
$\therefore \,\,\,I = \frac{1}{2}\int_{}^{} {\frac{{dt}}{t} = \frac{1}{2}\log t + c} $; $I = \frac{1}{2}\log (1 + {x^2}) + c$.
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